The present invention relates to a needle lift damper device in an injector for fuel injection, and a needle lift damping method. In particular, it relates to a device and method for damping needle valve lift in order to decrease the initial injection rate of a common rail injector in a diesel engine.
FIG. 4 shows an outline of a common rail-type fuel injection device in a diesel engine. As shown in the drawing, in this device, fuel within a fuel tank 1 is supplied to a high-pressure pump 4 through a filter 2 and a feed pump 3. After being pressurized to a high pressure (tens to hundreds of MPa) by the high-pressure pump 4, the fuel goes through a passage 5 and is stored in an accumulator called a common rail 6. The fuel inside the common rail 6 is supplied to each injector 8 through a fuel supply passage 7.
As shown in FIG. 5, a portion of the high-pressure fuel that is supplied to each injector 8 is supplied to a pressure control chamber 10 through a passage 9 and the remaining portion is supplied through a passage 11 to a fuel puddle 13 at the tip of a needle valve 12. The fuel pressure inside the pressure control chamber 10 is maintained and released by a relief valve 14. The relief valve 14 is depressed by a conventional spring 15 and closes a relief hole 16, maintaining the fuel pressure in the pressure control chamber 10. When an electromagnetic solenoid 17 is driven by an electric current, the relief valve 14 resists the spring 15 and is lifted up, thereby opening the relief hole 16 and releasing the fuel pressure in the pressure control chamber 10. Further, the needle valve 12 is constantly forced downwards by a spring 18.
In such injectors 8, when the electric current to the electromagnetic solenoid 17 is turned off, the relief hole 16 is closed by the relief valve 14 that is pressed down by the spring 15; and since the fuel pressure in the pressure control chamber 10 is maintained, the downward force on the needle valve 12 created by such fuel pressure and the spring 18 becomes greater than the upward force thereon created by the fuel pressure in the pressure-receiving portion 19 at the tip (fuel puddle 13) of the needle valve 12; and accordingly the needle valve 12 moves downward. Consequently, a conical portion 20 at the tip of the needle valve 12 is mounted to a seat 21, closing a spray hole 22 of the injector 8 so that fuel injection does not occur. thereon created by the fuel pressure in the pressure-receiving portion 19 at the tip (fuel puddle 13) of the needle valve 12; and accordingly the needle valve 12 moves downward. Consequently, a conical portion 20 at the tip of the needle valve 12 is mounted to a seat 21, closing a spray hole 22 of the injector 8 so that fuel injection does not occur.
Further, when the electromagnetic solenoid 17 is driven by an electric current, the relief valve 14 resists the spring 15 and is lifted up; and since the relief hole 16 is opened and the fuel pressure in the pressure control chamber 10 is released, the upward force on the needle valve 12 created by the fuel pressure in the pressure receiving portion 19 at the tip (fuel puddle 13) of the needle valve 12 becomes greater than the downward force thereon created by the fuel pressure and the spring 18; and accordingly the needle valve 12 lifts upward. Consequently, the conical portion 20 at the tip of the needle valve 12 becomes detached from the seat 21 and high pressure fuel is injected from the spray hole 22 of the injector 8. Note that the fuel flowing out of the pressure control chamber 10 is returned to the fuel tank 1 through a fuel return passage 23 (See FIG. 4).
In the above-mentioned injector 8, it is desirable that the needle valve 12 is made to lift upward comparatively smoothly (slowly). If the needle valve 12 is made to lift upwards comparatively smoothly, the initial injection rate of the fuel injected from the spray hole 22 decreases, and since the first ignition after an ignition delay occurs with a low injection rate and a small amount of fuel, a smooth first ignition can be guaranteed, resulting in less NOx emitted and a decrease in noise.
FIG. 6 shows an injector that is known to lift the needle valve 12 comparatively slowly (for example, Japanese Patent Application Laid-open No. S59-165858). Note that since this injector 8a has some constituent parts that are the same as the previously mentioned injector 8, identical reference numerals are used for the same constituent parts, and explanations are omitted. Only the different parts are explained.
In the injector 8a shown in FIG. 6, a member 24 is attached to the upper end of the needle valve 12, and the pressure control chamber 10 is formed above the member 24. The relief hole 16 is formed on the ceiling of the pressure control chamber 10. A seat 25 that is in a raised position is formed around the relief hole 16. The relief hole 16 is opened and closed by the relief valve 14, having an orifice hole 26 in its center, when it mounts to and disengages from the seat 25.
The relief valve 14 is pressed onto the seat 25 by a conventional spring 27, thereby closing the relief hole 16; and when fuel is supplied from a three-way valve 28, due to the fuel pressure, the relief valve 14 resists the spring 27 and is pushed downward, opening the relief hole 16. The three-way valve 28 is positioned in the passage 9 leading from the common rail 6 (see FIG. 4) to the pressure control chamber 10 and is switched over as appropriate between a state where X-Y are linked to each other and a state where Y-Z are linked to each other.
FIG. 6 shows the state when fuel injection has ceased. At this time, X-Y are linked to each other, the relief valve 14 is mounted to the seat 25, and the downward force on the needle valve 12 created by the fuel pressure inside the pressure control chamber 10 and the spring 18 is greater than the upward force thereon created by the fuel pressure in the fuel receiving portion 19 at the tip (fuel puddle 13) of the needle valve 12. Consequently, the needle valve 12 moves downward and the conical portion 20 is mounted to the seat 21, closing the spray hole 22 so that fuel injection does not occur. From this state, when the three-way valve 28 operates so that Y-Z are linked to each other, since the fuel in the pressure control chamber 10 is gradually squeezed from the orifice hole 26 in the relief valve 14 and flows out, the fuel pressure in the pressure control chamber 10 decreases at a smooth pace and the needle valve 12 lifts upward comparatively slowly. In this way lift damping of the needle valve is achieved and the initial injection rate from the spray hole 22 is decreased.
Subsequently, when the three-way valve 28 operates so that X-Y are linked to each other for a second time, since the fuel in the common rail 6 flows through passages 7 and 9 in a high-pressure state into the pressure control chamber 10, the relief valve 14 resists the spring 27 and is depressed due to the fuel pressure. The fuel flows into the pressure control chamber 10 in one burst and the fuel pressure in the pressure control chamber 10 rises at once, so the needle valve 12 moves downward rapidly. Consequently, the injection cut-off of the fuel injected from the spray hole 22 is improved.
However, in the above-mentioned injector 8a, since damping the lift of the needle valve 12 is achieved by mounting the relief valve 14 to the seat 25 as well as making the fuel in the pressure control chamber 10 leak out while being squeezed from the orifice hole 26, disturbance in the leak flow that occurs at the time of leakage from the orifice hole 26 can cause the relief valve 14 to vibrate and momentarily become dislodged from the seat 25.
When this occurs, since the fuel in the pressure control chamber 10 leaks not only from the orifice hole 26 but also from the gap between the relief valve 14 and the seat 25, the damping effect in respect of the lift of the needle valve 12 becomes lower than the design value and a sufficient damping effect is not obtained. Further, such a problem is intermittent on each occasion of leakage from the orifice hole 26 (or injection from the spray hole 22), thus making it difficult in fact to obtain a stable damping effect (initial injection rate reduction effect).
More specifically, in the above-mentioned injector 8a, the pressure control chamber 10 that controls the upward and downward movement (opening and closing) of the needle valve 12 also functions as a damping chamber for damping the needle valve 12. Therefore, in order to perform damping when the needle valve 12 is lifting upward, while it is necessary that the relief valve 14 is mounted to the seat 25 and is sealed, it is also necessary that the sealed portion (relief valve 14 and seat 25) is disengaged when the needle valve 14 is moving downward.
In this way, since the sealed portion (relief valve 14 and seat 25) is mounted together and disengaged during the upward and downward movement of the needle valve 12, when the needle valve 12 is lifting upward, as described above, the relief valve 14 vibrates and may momentarily become dislodged from the seat 25 due to the pressure variation of the pressure control chamber 10 that functions as a damping chamber, thereby making the seal defective.
It is an object of the present invention, which was designed with the foregoing circumstance in mind, to provide a needle lift damper device in an injector for fuel injection and a needle lift damping method that enables a stable damping effect to be consistently obtained.
A further object of the present invention is to provide a needle lift damper device in an injector for fuel injection and a needle lift damping method that enables a stable fuel leak to be consistently produced.
A further object of the present invention is to provide a needle lift damper device in an injector for fuel injection and a needle lift damping method that enables the initial injection rate of each injection to be stabilized.
The present invention is a damper device designed to achieve damping of the lift of a needle valve in an injector that lifts the needle valve that is depressed after receiving fuel pressure inside the pressure control chamber, by relieving the fuel pressure. It comprises a damper member slidably mounted to the needle valve; a damping chamber that becomes filled with fuel, formed between the damper member and the needle valve; a leak passage for extracting fuel from inside the damping chamber and leaking it outside the chamber; and a stopper member located above the damper member for restricting the lift position of the damper member.
According to the present invention, since the damper member is slidably mounted to the needle valve, the needle valve guides the damper member in an upward and downward movement and prevents vibration of the damper member. In such a way, a stable damping effect can be consistently produced.
It is desirable that the damper member is slidably inserted in an axial direction into a hole formed in the needle valve.
The stopper member is positioned above the needle valve and the pressure control chamber is defined therebetween, while the hole is formed to a prescribed depth axially from the upper surface of the needle valve, and the damper member is inserted into this hole from above and is able to move up and down in the pressure control chamber. The damping chamber is formed between the damper member and the hole, and it is desirable to form the leak passage passing through the damper member in an axial direction.
The upper end of the damper member is a flange that is larger in diameter than the hole and smaller in diameter than the upper surface of the needle valve and it is desirable that this flange is positioned above the hole and upper surface of the needle valve as well as being positioned inside the pressure control chamber.
It is desirable that a biasing means to impel the damper member upwards is formed in the damping chamber.
The biasing means consists of a coil spring, and it is desirable that a spring insertion hole having a prescribed depth is formed in the damper member facing upward from the bottom thereof, and that the coil spring is inserted into this spring insertion hole.
It is desirable that a relief passage, opening into the pressure control chamber to relieve the fuel pressure therein, is formed in the stopper member.
It is desirable that when the damper member abuts against the stopper member, the relief passage is prevented from communicating with the pressure control chamber and communicates with the damping chamber through the leak passage.
It is desirable that the fuel pressure is introduced into the pressure control chamber through the relief passage.
It is desirable that above the stopper member, a relief valve to open and close the exit of the relief passage and an driving means to drive the opening and closing of the relief valve are formed.
The driving means may consist of a spring and electromagnetic solenoid.
When the relief valve is closed and a prescribed period of time has elapsed, the pressure control chamber and the damping chamber reach a high pressure equal to the fuel pressure and the needle valve is depressed. Fuel injection is halted and the damper member abuts againststopper member. It is desirable that from this state, when the relief valve opens, the high-pressure fuel in the damping chamber flows through the leak passage and is gradually leaked into the relief passage, enabling the needle valve to lift up comparatively smoothly so that the initial injection is conducted comparatively smoothly. It is desirable that from this state, when the relief valve is closed, the fuel pressure supplied to the relief passage acts on the damper member such that the damper member and the needle valve are depressed together, making the needle valve move downward comparatively rapidly and halting the fuel injection comparatively rapidly.
When applied to a common rail-type fuel injection device in a diesel engine, the fuel pressure can be supplied from the common rail.
The present invention is also a method for damping the lift of the needle valve in an injector that lifts the needle valve that is depressed after receiving fuel pressure in the pressure control chamber, by relieving the fuel pressure. A damper member is slidably mounted to the needle valve; a damping chamber that becomes filled with fuel is formed therebetween; a leak passage for extracting fuel from inside the damping chamber and leaking it outside the chamber is formed; and a stopper member positioned above the damper member for restricting the lift position thereof is formed. When the needle valve lifts, the fuel in the damping chamber is extracted and leaked through the leak passage, thereby damping the lift of the needle valve.
It is desirable that the damper member is slidably inserted in an axial direction into a hole formed in the needle valve.
The stopper member is positioned above the needle valve and the pressure control chamber is defined therebetween, while the hole is formed to a prescribed depth from the upper surface of the needle valve in an axial direction, and the damper member is inserted into this hole from above and is able to move up and down in the pressure control chamber.
The damping chamber is formed between the damper member and the hole, and it is desirable to form the leak passage so as to pass through the damper member in an axial direction. It is desirable that the damper member is impelled upward by a biasing means formed in the damping chamber.
It is desirable that a relief passage, opening into the pressure control chamber is formed axially so as to pass through the stopper member, and the fuel pressure in the pressure control chamber is relieved by this relief passage.
The relief passage and leak passage are positioned on the same axis and when the damper member abuts against the stopper member, the relief passage is prevented from communicating with the pressure control chamber, but instead communicates with the damping chamber through the leak passage; and it is desirable that before the needle valve begins to lift, the damper member is made abut against the stopper member.
When the relief valve is closed and a prescribed period of time has elapsed, the pressure control chamber and the damping chamber reach a high pressure equal to the fuel pressure, and the needle valve is depressed. Fuel injection is halted and the damper member abuts against the stopper member.
It is desirable that from this state, when the relief valve opens, the high-pressure fuel in the damping chamber flows through the leak passage and is gradually leaked into the relief passage, enabling the needle valve to lift up comparatively smoothly, with the result that the initial injection is carried out comparatively smoothly.
It is desirable that from this state, when the relief valve is closed, the fuel pressure supplied to the relief passage acts on the damper member so that the damper member and the needle valve are depressed together, making the needle valve move downward comparatively rapidly with the result that fuel injection is halted comparatively rapidly.
When applied to a common rail-type fuel injection device in a diesel engine, the fuel pressure can be supplied from the common rail.